The present invention relates to infrared radiation detector cells for detecting infrared radiation, in particular, to thermal-type infrared radiation detector cells for detecting infrared radiation by converting it to heat, and further relates to image capture devices incorporating such thermal-type infrared radiation detector cells. Specifically, the present invention relates to thermal-type infrared radiation detector cells with an increased infrared radiation absorption rate and reduced irregularities in detection sensitivity, and further relates to image capture devices incorporating such thermal-type infrared radiation detector cells.
Conventionally, there are a large variety of infrared radiation detection methods being developed based on different principles and adopted in the working of various types of infrared radiation detector cells for detecting infrared radiation. Typically used among these methods is to convert infrared radiation energy into electrical signals by means of a band gap of semiconductor materials, i.e., to exploit photon effects of infrared radiation energy, because the method exhibits high sensitivity and quick response. Infrared radiation detector cells incorporating the method is called a quantum type.
Despite these advantages, the quantum-type infrared radiation detector cell is only capable of detecting a limited range of wavelengths. To detect those infrared rays with very low infrared radiation energy, e.g., those with long wavelengths, semiconductor materials used for the detection of infrared radiation need to be kept at an extremely low temperature. For example, in the quantum-type infrared radiation detector cell, the semiconductor material needs to be kept around 77K, that is, approximately xe2x88x92196xc2x0 C., using liquid nitrogen. This requirement makes infrared radiation detector devices cumbersome to handle and difficult to make smaller due to the use of liquid nitrogen for cooling.
Another type of infrared radiation detector cells developed based on different principles to detect infrared radiation is of thermal types that do so by converting infrared radiation energy into heat. In a thermal-type infrared radiation detector cell, as a detector cell material absorbs infrared radiation energy and converts it to heat, the detector cell material heats up and thus changes its physical properties (electrical resistance, pyroelectricity, etc.). By means of the detection of these changes, the infrared radiation is detected.
Accordingly, in the thermal-type infrared radiation detector cell, unlike in its quantum-type counterpart, there is no need for semiconductor materials used for the detection of infrared radiation to be kept at extremely low temperatures. Thus, the thermal-type infrared radiation detector cell can be used at room temperature and offers room for possible reduction in size through the omission of cooling means, thereby getting wide attention for its practical performance in recent years.
However, some objects generate so little heat in the thermal-type infrared radiation detector cell that the resultant temperature elevation is as small as 0.01xc2x0 C. or even smaller, making it difficult for the thermal-type infrared radiation detector cell to detect infrared radiation. To solve this problem, some thermal-type infrared radiation detector cells incorporate such a structure that exhibits an increased infrared radiation absorption rate, and thus increase the elevation in their temperature and enhance the sensitivity in detecting infrared radiation to a greatest extent possible.
To solve these problems, the typical thermal-type infrared radiation detector cell typically including a diaphragm structure in which a diaphragm structural body for detecting infrared radiation is separated by a predetermined gap from a semiconductor substrate on which there is provided an integrated circuit (or a signal integrated circuit) electrically connected to the diaphragm structural body by metal wiring. The structure enhances the thermal insulation between the diaphragm structural body (infrared radiation receiving section, or sensor section) for detecting infrared radiation and the semiconductor substrate with an integrated circuit, thereby successfully achieving high sensitivity in the detection of infrared radiation.
To further improve on the infrared radiation absorption rate, the thermal-type infrared radiation detector cell incorporating the diaphragm structure normally employs one of two techniques: namely, (a) the selective use of substance exhibiting high infrared radiation absorption, and (2) the adoption of multiple reflection of infrared rays. According to technique (1), arrangement (a) is employed whereby a thin film (infrared radiation absorbing film) composed of a material exhibiting a high infrared radiation absorption rate is provided on the surface of the diaphragm structure. According to technique (2), arrangement (b) is employed whereby, in addition to arrangement (a), an infrared radiation reflector film is provided on the semiconductor substrate below the diaphragm structure.
FIGS. 15(a) and 15(b) show an example of arrangement. (a) adopted in a thermal-type infrared radiation detector cell incorporating technique (1). A diaphragm structural body 101a is positioned over a semiconductor substrate 108 on top of which there is provided an integrated circuit (not shown), so as to be separated from the semiconductor substrate 108 by a predetermined gap. An infrared radiation absorbing film 107a is also provided on the surface of the diaphragm structural body 101a (arrangement (a)).
FIGS. 16(a) and 16(b) show an example of arrangement (b) adopted in a thermal-type infrared radiation detector cell incorporating technique (2). Arrangement (b) is basically identical to arrangement (a) employed in the thermal-type infrared radiation detector cell shown in FIGS. 15(a) and 15(b), except that arrangement (b) additionally includes an infrared radiation reflector film 106 on the surface of the semiconductor substrate 108.
The arrangements employed in the thermal-type infrared radiation detector cell will be briefly discussed below. The diaphragm structural body 101a or 101b are each constituted by a second silicon oxide film 102, a thermally variable resistor film 103 and a metal wiring film 104 provided on the second silicon oxide film 102 in a predetermined pattern, and a third silicon oxide film 105 covering these films. Infrared radiation absorbing films 107a and 107b composed of a material processing a high infrared radiation absorption rate are provided on the third silicon oxide film 105 according to techniques (1) and (2) respectively (arrangement (a)).
A first silicon oxide film 109 is provided on the semiconductor substrate 108 on top of which there is provided an integrated circuit (not shown). According to technique (2), an infrared radiation reflector film 106 composed of a substance capable of substantially entirely reflecting infrared rays is provided on the first silicon oxide film 109 so as to oppositely face the diaphragm structural body 101b (arrangement (b)).
It should be noted that as shown in FIG. 15 (a) and FIG. 16(a), both diaphragm structural bodies 101a and 101b are supported by legs 110 and electrically connected to the semiconductor substrate 108 via the metal wiring film 104 contained in the legs 110. As shown in FIG. 15(a) and FIG. 16(a), almost all of the surfaces of the diaphragm structural bodies 101a and 101b serve as first infrared radiation receiving areas (enclosed by broken lines).
In the thermal-type infrared radiation detector cells including arrangement (a) and (b), incident infrared rays shine down on the infrared radiation absorbing films 107a and 107b in the first infrared radiation receiving areas of the diaphragm structural bodies 101a and 101b respectively. Under these conditions, in technique (1), infrared rays are substantially entirely absorbed by the infrared radiation absorbing film 107a of a sufficiently increased thickness.
In technique (2), the infrared rays are partly reflected by, and partly pass through, the infrared radiation absorbing film 107b, with the rest of the infrared rays being converted to Joule heat by the electrical resistance of, and subsequently absorbed by, the infrared radiation absorbing film 107b. Having passed through the infrared radiation absorbing film 107b, the infrared rays pass through the diaphragm structural body 101b, that is, through the third silicon oxide film 105, the thermally variable resistor film 103, and the second silicon oxide film 102, and reach the infrared radiation reflector film 106.
The infrared rays are then entirely reflected back toward the diaphragm structural body 101b from the infrared radiation reflector film 106 with a phase delay of xcfx80, because the infrared radiation reflector film 106 is a low-resistance complete reflection film composed with a metal with a sheet resistance not exceeding a few xcexa9/xe2x96xa1. The reflected infrared rays take the path in reverse direction, passing through the diaphragm structural body 101b. As having reached the infrared radiation absorbing film 107b disposed on the top of the diaphragm structural body 101b, the infrared rays are again reflected, passed, and absorbed by the infrared radiation absorbing film 107b. 
As detailed above, the incident infrared rays entering the diaphragm structural body 101b are repeatedly reflected in the diaphragm structural body 101b and do not leak out, effectively improving the infrared radiation absorption rate of the thermal-type infrared radiation detector cell. In a thermal-type infrared radiation detector cell incorporating the diaphragm structural body 101b, that is, employing technique (2), the infrared radiation absorption rate per unit area is determined by the relationships among the reflection, passage, and absorption of infrared rays in the diaphragm structural body 101b. 
A specific example of technique (2) is disclosed in Japanese Laid-Open Patent Application No. 10-111178/1998. In this example, the infrared radiation absorbing film is separated from a reflector film by a predetermined distance by means of the interposition of one or more intermediate films of a predetermined thickens between the infrared radiation absorbing film and the reflector film underneath. In this example the predetermined distance, d, is defined as follows:
d=(2Nxe2x88x921)xc3x97xcex/(4n)
wherein N is a positive integer, xcex is the wavelengths of infrared rays detected, and n is the refractive index of the film with a predetermined thickness.
The arrangement enables the distance by which the reflector film is separated from the infrared radiation absorbing film to be maintained at a fixed value, and improves sensitivity by reducing the thickness of the diaphragm structural body 101b, since an increase in the refractive index of the intermediate film allows a reduction in the predetermined distance.
However, generally, a structure with high infrared radiation absorption and a manufacturing process to incorporate such a structure in the thermal-type infrared radiation detector cell are so complex to reduce the yields and increase cost. Both techniques (1) and (2) suffer these problems.
In addition to these problems, thermal-type infrared radiation detector cells fabricated by technique (1) entail slow response due to its enlarged size and hence increased thermal capacity. As a result, an infrared radiation image capture device incorporating such a thermal-type infrared radiation detector cell fails to produce a satisfactory level of performance.
Specifically, according to technique (1), the infrared radiation absorbing film 107a including arrangement (a) should be composed of material capable of absorbing infrared radiation efficiently, such as gold black and organic materials; however, it is difficult to fabricate a thin film from the material. Contradictory to the requirement to reduce the film thickness made of the material, the infrared radiation absorbing film 107a needs to have a thickness of at least a few xcexcm to exhibit an infrared radiation absorption rate of 80% or greater. The thickness imparts too large thermal capacity for the infrared radiation detector cell to produce quick response, which presents an obstacle in high speed imaging. For these reasons, the thermal-type infrared radiation detector cell incorporating technique (1) is rarely applied in infrared radiation image capture elements.
According to technique (2), the diaphragm structural body 101b including arrangement (b) produces internal multiple reflection and thereby does not allow infrared rays to leak out. This allows the infrared radiation absorbing film 107b incorporating arrangement (a) to have a reduced thickness as small as a few hundred nm and hence to have a reduced thermal capacity. Further, theoretically, the infrared radiation absorption rate reaches almost 100% if the distance by which the diaphragm structural body 101b incorporating arrangement (a) is separated from the semiconductor substrate 108 incorporating arrangement (b) is equal to xc2xcn times the wavelength of the infrared rays absorbed, and the sheet resistance of the infrared radiation absorbing film 107b incorporating arrangement (a) is equal to 377 xcexa9.
However, technique (2) entails three major structural problems caused by (i) the metal wiring film 104, (ii) the infrared radiation reflector film 106, and (iii) the control of the distance between the infrared radiation absorbing film 107b and the infrared radiation reflector film 106. These problems are discussed in detail in the following.
(i) Problems Arising from the Metal Wiring Film 104
As shown in FIG. 16(a), in the thermal-type infrared radiation detector cell, a metal wiring film 104 is formed along each side of the thermally variable resistor film 103 to measure the resistance of the thermally variable resistor film 103. The metal wiring film 104 is typically composed of aluminum, and thus cause undesired reflection of infrared rays.
In other words, the diaphragm structural body 101b is designed so that the infrared radiation reflector film 106 reflects infrared rays in such a manner that the infrared rays are ultimately absorbed. Meanwhile, the metal wiring film 104 reflects infrared rays in such a manner that none of the infrared rays are absorbed. So, the parts of the thermally variable resistor film 103 covered with the metal wiring films 104 absorb almost no infrared rays.
The net infrared radiation absorption by the thermal-type infrared radiation detector cell is determined by the infrared radiation absorption rate in the infrared radiation receiving area I multiplied by the infrared radiation absorption area ratio. The infrared radiation absorption area ratio is defined as the ratio (fill factor) of the infrared radiation receiving area I to the size (cell size) of the thermal-type infrared radiation detector cell. For example, the thermal-type infrared radiation detector cell shown in FIG. 16(a) has a fill factor of about 0.5, and the infrared radiation absorption rate in the infrared radiation receiving area I is 80%. Accordingly, the net infrared radiation absorption by the thermal-type infrared radiation detector cell is given by:
80%xc3x970.5=40%
The figure indicates that about 40% of incident infrared rays is absorbed.
ii) Problems Caused by the Infrared Radiation Reflector Film 106
The infrared radiation reflector film (low-resistance complete reflection film) 106 capable of reflecting the infrared rays having passed through the diaphragm structural body 101b is formed on a top surface of a first silicon oxide film 109, serving as a protection film, formed on the semiconductor substrate 108 on which there is provided an integrated circuit. Therefore, a separate step is necessary to fabricate the infrared radiation reflector film 106, which adds to the time required for the whole manufacturing process. Besides, the step to form the infrared radiation reflector film 106 must include alignment and etching, which adds to the total cost.
(iii) Problems in the Control of the Distance Between the Infrared Radiation Absorbing Film 107b and the Infrared Radiation Reflector Film 106
According to the principles based on which the infrared radiation absorbing film 107b absorb infrared rays, the infrared radiation absorption rate is influenced by the distance between the infrared radiation absorbing film 107b (arrangement (a)) and the infrared radiation reflector film 106 (arrangement (b)). Thus, the control of the distance between these thin films is essential. However, the stress of the thin films are extremely difficult to control, compared to the thicknesses of the thin films. Therefore, the thicknesses can be successfully controlled to form desirably thin films, whereas the control of the stress is likely to fail. This causes warping of the diaphragm structural body 101b and hence irregular distance. The resultant, actual infrared radiation absorption rate is thus inferior to that originally designed. For example, a thermal-type infrared radiation detector cell designed to absorb infrared rays of wavelengths in a range from 8 xcexcm to 12 xcexcm is. theoretically capable of achieving a 100% infrared radiation absorption rate, but in practical use exhibits only an unimpressive rate of about 80%.
Besides, the distance becomes irregular at any given point in a chip matrix. Therefore, when applied in an infrared radiation image capture element, the thermal-type infrared radiation detector cells incorporating technique (2) entail another problem of irregularities in in-plane angles, which negatively affects image quality.
A further problem is found in Tokukaihei 10-111178 which is an example of technique (2). According to the disclosure, the infrared radiation absorbing film is separated from the reflector film by a predetermined distance, d, by means of the interposition of one or more intermediate films. This structure does enable the distance by which the reflector film is separated from the infrared radiation absorbing film to be maintained at a fixed value. However, at least three different kinds of films (namely, the infrared radiation absorbing film, the reflector film, and the intermediate film) need to be formed, and the thicknesses of all of them need to be controlled as detailed in the foregoing. These requirements add to the number of steps and cost required in the manufacture.
In view of the above problems, the present invention has an object to present thermal-type infrared radiation detector cells capable of achieving increased infrared radiation absorption and being manufactured in fewer and simpler steps.
Another object of the present invention is to present thermal-type infrared radiation detector cells including a diaphragm structure of a small thermal capacity, capable of achieving an increased infrared radiation absorption rate and reduced irregularities in sensitivity without adding largely to the number of steps in manufacturing process.
A thermal-type infrared radiation detector cell in accordance with the present invention has a diaphragmatic structure constituted by:
a semiconductor substrate on which there is provided an integrated circuit; and
a diaphragm structural body electrically connected to, and separated by a predetermined gap from, the semiconductor substrate,
wherein the diaphragm structural body includes at least:
a thermally variable resistor film changing resistance thereof upon reception of infrared rays; and
metal wiring films electrically connected to the thermally variable resistor film and also to a terminal section in the substrate,
wherein the metal wiring films are formed so as to constitute an infrared radiation reflector film for reflecting incident infrared rays so that the thermally variable resistor film can receive the reflected infrared rays in the diaphragm structural body.
According to the arrangement, the metal wiring films are constituted by an infrared radiation reflector film capable of reflecting infrared rays; therefore, unlike prior art, the metal wiring films in the diaphragm structural body do not interrupt the infrared rays entering the infrared radiation reflector film placed on a side of the diaphragm structural body opposite to the substrate, and thereby provides an increased effective absorption area where the diaphragm structural body can absorb infrared rays. Further, since the metal wiring film doubles as the infrared radiation reflector film, no separate step is necessary to fabricate a infrared radiation reflector film, facilitating the manufacturing process of the cell.
In the thermal-type infrared radiation detector cell arranged in this manner, it is preferable if the metal wiring films are formed so as to cover a substantial entirety of either a top surface or a bottom surface of the thermally variable resistor film.
According to the arrangement, after being reflected by the metal wiring films, the infrared rays having passed through the diaphragm structural body interferes with reflected light from the surface of the high refractive index film (dielectric film) at this surface, having its reflection substantially offset. The infrared rays are therefore efficiently absorbed by reflection and interference in the diaphragm structural body, and the diaphragm structural body greatly increases its absorption of infrared rays.
It is preferable if the metal wiring films are composed of a material capable of reflecting 95% or more of incident infrared rays entering the infrared radiation receiving section. Titanium and aluminum are good examples.
In the thermal-type infrared radiation detector cell arranged in this manner, it is preferable if the diaphragm structural body has such a substantially planar shape to provide a two-dimensionally spreading infrared radiation receiving area where infrared rays are received; and the metal wiring films are formed so as to two-dimensionally spread substantially corresponding to the infrared radiation receiving area.
This structure further ensures the function of the metal wiring films as an infrared radiation reflector film. The thermally variable resistor film may be provided on the metal wiring films, either on their top or bottom surface.
It is preferable if the thermal-type infrared radiation detector cell arranged in this manner further includes an insulating layer interposed between the thermally variable resistor film and the metal wiring films. A suitable insulating layer is primarily composed of silicon oxide.
In thermal-type infrared radiation detector cell arranged in this manner, it is preferable if the diaphragm structure is provided with an infrared ray entry surface separated from the surfaces of the metal wiring films by a distance substantially equal to xc2xcn times the wavelengths of incident infrared rays, where n is the refractive index of a substance interposed between the infrared ray entry surface and the surfaces of the metal wiring films.
According to the arrangement, the infrared rays reflected by the metal wiring films interferes with reflected light from the surface of the high refractive index film at this surface, having its reflection substantially offset and being absorbed by the infrared radiation absorbing film. This ensures the absorption of infrared rays by means of reflection and interference within the diaphragm structural body, and the diaphragm structural body greatly increases its absorption of infrared rays.
Another thermal-type infrared radiation detector cell in accordance with the present invention has a diaphragm structure constituted by
a semiconductor substrate on which there is provided an integrated circuit; and
a diaphragm structural body electrically connected to, and separated by a predetermined gap from, the semiconductor substrate,
wherein the diaphragm structure further includes a high refractive index film and an infrared radiation reflector film provided beneath the high refractive index, and
the high refractive index film has a thickness, d, given approximately by
d=xcexxc3x97{1/(4xc3x97n)}
where n is a refractive index of the high refractive index film and xcex is the wavelengths of infrared rays absorbed.
According to the arrangement, the adoption of a diaphragm structure keeps the thermal conductance low with the equation being substantially satisfied in the diaphragm structure. Therefore, the diaphragm structure does not allow Joule heat produced by infrared rays to escape therefrom, and the reflection of infrared rays by the surface of the diaphragm structure is offset by interference effects. Thus, infrared rays are not allowed to escape from the diaphragm structure. The distance separating the high refractive index film from the reflector film, which influence interference effects greatly, is controlled by means of the thickness of the high refractive index film, and therefore is constant.
For these reasons, the thermal-type infrared radiation detector cell exhibits much higher and constant infrared radiation absorption rate than conventional counterparts, and thereby achieves more constant sensitivity The use of a high refractive index film enables the diaphragm structure to have a greatly reduced thickness, preventing increase in the thermal capacity of the thermal-type infrared radiation detector cell. In other words, the thermal capacity of the diaphragm structure can be greatly reduced compared to conventional technologies. As a result, an element can be prepared with a better sensitivity and shorter response time than those of conventional technologies.
Further, according to the arrangement, no infrared radiation absorbing film needs to be formed, and an increase in efficiency in infrared radiation absorption can be achieved structurally through control of the thickness of the high refractive index film alone. So, no additional steps are required in the manufacturing process. Rather, the manufacturing process can be simplified and the manufacturing cost is reduced, due to the fact that no infrared radiation absorbing film needs to be formed. The thermal-type infrared radiation detector cell thereby boasts excellent performance and are prepared at a reduced cost.
In the thermal-type infrared radiation detector cell arranged in the above manner, it is preferable if the diaphragm structural body further includes a thermally variable resistor film that changes its electric resistance with temperature variations and metal wiring films electrically connected to the thermally variable resistor film.
According to the arrangement, the infrared radiation absorption by the high refractive index film increases temperature. The rise in temperature then changes the electric conductance, hence resistance, of the thermally variable resistor film changes accordingly. As a result, infrared rays absorbed by the high refractive index film are converted to electric signals, passed through the metal wiring films electrically connected the thermally variable resistor film, and detected efficiently. Therefore, it is better ensured that infrared rays are detected.
In the thermal-type infrared radiation detector cell arranged in the above manner, it is preferable if there is provided an insulating layer between the infrared radiation reflector film and the thermally variable resistor film.
According to the arrangement, the provision of an insulating layer between the infrared radiation reflector film and the thermally variable resistor film prevents heat, which is intended to heat the thermally variable resistor film, from flowing through the highly heat conductive infrared radiation reflector film. Thus the thermally variable resistor film is efficiently heated. As a result, the thermal-type infrared radiation detector cell has improved sensitivity.
In the thermal-type infrared radiation detector cell arranged in the above manner, it is preferable if there is provided at least a thermally variable resistor film between the high refractive index film and the infrared radiation reflector film.
According to the arrangement, the thermally variable resistor film is placed closely to the high refractive index film producing heat by means of infrared radiation absorption. Therefore, the heat from the high refractive index film is prevented from flowing into the infrared radiation reflector film before reaching the thermally variable resistor film. Thus the thermally variable resistor film is efficiently heated. As a result, the thermal-type infrared radiation detector cell has improved sensitivity.
In the thermal-type infrared radiation detector cell arranged in the above manner, it is preferable if the infrared radiation reflector film doubles as the metal wiring films.
According to the arrangement, the metal wiring films double as the infrared radiation reflector film; therefore, no step is required to deposit an infrared radiation reflector film and fabricate it into a predetermined shape. Thus the thermal-type infrared radiation detector cell has a simplified structure, and is manufactured at a further reduced cost.
In the thermal-type infrared radiation detector cell arranged in the above manner, it is preferable if there is provided an insulating layer between the high refractive index film and the infrared radiation reflector film.
According to the arrangement, the high refractive index film is insulated from the infrared radiation reflector film; therefore, no sense current branches out from the thermally variable resistor film to the high refractive index film. Thus, changes in the resistance of the thermally variable resistor film caused by infrared radiation absorption can be efficiently detected, and the thermal-type infrared radiation detector cell has further improved sensitivity.
Besides, according to the arrangement, no sense current branches out to the high refractive index film; therefore, the heat resistance variation of the thermally variable resistor film can be increased by increasing its resistivity. As a result, the thermal-type infrared radiation detector cell has further improved sensitivity. Further, since no sense current branches out to the high refractive index film, the high refractive index film itself can have a reduced resistivity. Therefore, the high refractive index film can have an increased refractive index, and thus reduced thickness. As a result, the thermal-type infrared radiation detector cell has improved time resolution.
In the thermal-type infrared radiation detector cell arranged in the above manner, it is preferable if the diaphragm structure includes a supporting member for supporting the diaphragm structural body over the semiconductor substrate while maintaining a predetermined gap therebetween, wherein
the metal wiring films are provided on the supporting member, and there is provided an insulating layer to cover the metal wiring films formed on at least the supporting member.
According to the arrangement, the insulating layer covers the metal wiring films on the supporting member, and thereby provides protection to the normally exposed metal wiring films on the supporting member. As a result, the thermal-type infrared radiation detector cell has improved environmental insusceptibility.
In the thermal-type infrared radiation detector cell arranged in the above manner, it is preferable if the high refractive index film is primarily composed of either silicon or germanium.
In the thermal-type infrared radiation detector cell arranged in the above manner, the high refractive index film may double as the thermally variable resistor film.
According to the arrangement, the dues role of the high refractive index film as the thermally variable resistor film enables omission of the step to deposit an infrared radiation reflector film and fabricate it into a predetermined shape. Thus the thermal-type infrared radiation detector cell has a simplified structure, and is manufactured at a further reduced cost. In the arrangement, the high refractive index film is, suitably, composed primarily of silicon.
Another thermal-type infrared radiation detector cell in accordance with the present invention includes:
a semiconductor substrate on which there is provided an integrated circuit; and
a substantially planar diaphragm structural body electrically connected to, and separated by a predetermined gap, from the semiconductor substrate,
wherein the diaphragm structural body is provided with at least: an infrared ray entry surface through which infrared rays enter; and an infrared radiation reflector surface by which infrared rays having entered the diaphragm structural body are reflected, the infrared radiation reflector surface being disposed beneath the infrared ray entry surface, and
the infrared ray entry surface is separated from the infrared radiation reflector surface by a distance specified substantially equal to xc2xcn times the wavelengths of incident infrared rays, where n is a refractive index of a substance interposed between the infrared ray entry surface and the infrared radiation reflector surface.
According to the arrangement, with respect to the infrared rays having been reflected either by the metal wiring films or by infrared radiation reflector film, the reflection by the infrared ray entry surface is substantially offset. Therefore, infrared rays are absorbed by means of reflection and interference in the infrared radiation receiving section, and no separate infrared radiation absorbing film needs to be formed. As a result, the thermal-type infrared radiation detector cell absorbs a greater amount of infrared rays, thus improves sensitivity in detecting infrared rays, and has a simplified structure.
An image capture device in accordance with the present invention incorporates a thermal-type infrared radiation detector cell arranged in one of the above manners. According to the arrangement, thermal-type infrared radiation detector cells arranged in one of the above manners is used to constitute image capture elements; therefore, pixels exhibit infrared radiation absorption rates that are far more constant in the infrared radiation image capture element than in the image capture device incorporating conventional infrared radiation detector cells. Consequently, the image capture device in accordance with the present invention has sensitivity that varies less from pixel to pixel, and capable of capture higher quality images than conventional counterparts.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.